The use of an inflatable cuff to occlude blood flow into a subject's limb, thereby providing a bloodless surgical field in the portion of the limb distal to the cuff over a time period suitably long for the performance of a surgical procedure, is well known in surgical practice. When employed to provide a bloodless surgical field, occlusive cuffs constitute one element of a surgical tourniquet system. Tourniquet systems typically include the following basic elements: a source of pressurized gas, an inflatable cuff for encircling a limb at a selected location, and a pressure regulating mechanism for controlling and maintaining the pressure of gas in the inflatable cuff and thus the pressure applied by the cuff to the limb which the cuff encircles. The recent advent of automatic tourniquet systems which employ digital electronic technology in the regulation of pressure and in the detection of certain hazardous conditions has led to significant improvements in the safety and accuracy of surgical procedures performed with an occlusive cuff applied proximally on a limb. These automatic tourniquet systems typically allow the surgeon to safely maintain a constant inflation pressure in the inflatable cuff which he or she estimates to apply pressures to the limb near the minimum required to safely occlude blood flow past the cuff. Recently, McEwen has described, in the U.S. patents and patent applications cited below, improved automatic tourniquet systems which provide for sensing and regulation of the pressures actually applied to the limb by a cuff, in contrast to merely sensing and regulation of the inflation pressure in the cuff.
However, despite improvements in electronic pressure regulation and applied pressure sensing, major limitations exist with respect to safety and efficacy of occlusive cuffs used as part of automatic tourniquet systems. These limitations in prior art occlusive cuffs have persisted despite the increasing use of such cuffs in more demanding surgical procedures, particularly those involving the use of intravenous regional anesthesia (IVRA). In surgical procedures performed under IVRA, the occlusive cuff must be effective in preventing the flow of blood into the field of surgical dissection as well as preventing the premature release of potentially toxic intravenous anesthetics from the veins of the operative limb into the general circulation.
In the design of most prior art cuffs, little attention has been paid to the actual spatial distribution of pressures applied to the limb beneath the cuffs, in both a circumferential direction around the limb, and a direction along the longitudinal axis of the limb, when the cuffs are inflated to various inflation pressures. This lack of attention has largely been due to the lack of suitable pressure transducers for measuring the applied pressures. However, in connection with the present invention, the biomedical pressure transducer described by McEwen in U.S. Pat. No. 4,869,265 was used as a tool to evaluate the ranges of pressures applied to limbs by a large number of prior art cuffs, and was used as a tool in the development and evaluation of the improved occlusive cuff described hereunder.
By using the McEwen biomedical pressure transducer to measure the pressures applied by a representative selection of prior art cuffs which overlap on themselves around limbs, major variations were found in the pressures applied in a circumferential direction around the limbs beneath the cuffs. In particular, the greatest pressure variations were found in the region of the overlap, where the pressure actually applied to the limb could be much less than the inflation pressure of the cuffs, thus creating low pressure pathways longitudinally for arterial blood to enter the limb, or for IVRA anesthetic agents to exit the limb. Significantly, prior art cuffs having the greatest cross-sectional thicknesses were found to create the greatest pressure discontinuities in the region of the overlap, and cuffs having less cross-sectional thicknesses had less pressure variations circumferentially in the region of the overlap.
Also by using the McEwen biomedical pressure transducer, it was possible to measure the pressures applied to limbs beneath prior art cuffs in a longitudinal direction along the limb, between the proximal and distal edges of the cuff, at selected locations around the circumference. Again, significant differences in longitudinally applied pressures were found in prior art cuffs having different designs. Despite the information in the prior art that shows that the magnitude and distribution of pressures longitudinally beneath cuffs affects the probability of nerve injury beneath the cuff, little attention has previously been paid to the design of cuffs which permit optimal, desirable or selectable distributions of pressures to be applied in a longitudinal direction beneath such prior art cuffs.
Limitations also exist in the safety of prior art cuffs. At present, overlapping occlusive cuffs known in the prior art generally incorporate a single means of securing the cuff around the limb, with no additional securing means functioning independently to hold the cuff in place should the first securing means fail. No overlapping cuff in the prior art known to the applicant has a secondary circumferential securing means for independently securing the overlapped cuff circumferentially around a limb so that, if the primary means for securing the cuff around the limb were to fail for any of a variety reasons, the overlapped cuff would continue to apply pressure to the limb safely for the period required to complete a surgical procedure. Almost all cuffs in the prior art are designed to overlap on themselves around limbs, and use only a primary securing means, such as a pair of mating strips of hook and loop material, for securing circumferentially. Dual-bladder cuffs known in the prior art for use in IVRA do use two separate sets of securing means, but they are intended for securing two separate bladders arranged longitudinally on the limb; if one of these sets of securing means fails, the safety and efficacy of the inflatable bladder beneath that set of strips is significantly affected. The absence of an independent, secondary circumferential securing means in overlapping cuffs of the prior art significantly limits their safety, especially in critical surgical procedures where continued maintenance of a bloodless field is essential, and in other procedures involving IVRA where the cuff must keep anesthetic agents in the limb and out of systemic circulation for a specified minimum time period.
Overlapping occlusive cuffs in the prior art generally include a stiffener cut from a sheet of flexible thermoplastic material such as polyethylene, polypropylene, or nylon, to constrain the bladder of the cuff, reduce the tendency of the inflated cuff to roll distally down the limb, and direct inflation inwardly toward the limb when the bladder is pressurized. The choice of materials and the physical dimensions of prior art stiffeners have often been arbitrary, or based on factors other than how the physical characteristics of these stiffeners would affect the pressures applied longitudinally and circumferentially to underlying limbs. Also, such prior art stiffeners have generally been integrated physically into the cuffs during manufacture so that, in cross-section, the stiffeners represent one integral layer of a multi-layer structure. One result is that such prior art cuffs have significant cross-sectional thickness, producing significant applied pressure discontinuities in their overlapping regions, as described above. Such prior art cuffs are relatively rigid longitudinally across their width dimension, which limits their conformance to different limb shapes and can produce undesirable longitudinal pressure distributions. Also, such prior art cuffs are relatively rigid along their length, which increases the difficulty that clinical staff have in attempting to bend such cuffs around limbs to snugly encircle them.
Most cuffs of the prior art employ Luer-type connectors to attach the cuffs to tubing connected to the pressure regulators of automated tourniquet systems. These Luer-type connectors have inherent safety limitations, because they have no secondary locking mechanism and they permit easy, inadvertent gas leaks and disconnection as a result of rotation of the tubing with respect to the cuff. Further safety limitations of overlapping cuffs of the prior art related to the absence of markings on the cuffs indicating aspects of the recommended, safe and efficacious use of the cuffs. For example, most prior art cuffs do not include markings which provide guidance as to the best choice of cuff, taking into account the shape, circumference and available length of a patient's limb, nor are markings generally included to assist in the optimal setting of inflation pressure or proper cuff usage.
An object of the present invention is to provide an overlapping occlusive cuff having secondary safety securing means for improved safety, comprising: an inflatable bladder for encircling and overlapping on itself around a limb, bladder securing means for engaging to secure the overlapping bladder around the limb with the bladder inflated to a pressure sufficient to occlude flow in blood vessels in the limb encircled by the bladder, and secondary safety securing means for securing the overlapping bladder around the limb independently of the bladder securing means such that the bladder remains overlapped and secured if the bladder securing means is not engaged or becomes ineffective while the bladder is inflated. A related object is to provide an operator with a visible indication on the cuff of a parameter affecting the safety or efficacy of the cuff, such as which cuff to select for best performance, or what inflation pressure is recommended, in a particular situation. Another related object for improved safety is to provide a cuff with locking connector means to connect the inflatable bladder to a tube containing pressurized gas while allowing bidirectional rotation of the tube with respect to the bladder until an operator disconnects the bladder from the tube by a combination of manual actuations.
Another object of the present invention is to provide an overlapping occlusive cuff having separately overlapping bladder and stiffener for improved application of pressure in a substantially circumferential direction around the limb, comprising: an inflatable bladder with a length sufficient for encircling and overlapping on itself around the limb, bladder securing means for securing the overlapping bladder around the limb, and stiffening means superimposed on the overlapping region of the bladder for directing the bladder in that region toward the limb when the bladder is inflated. A related object is to fabricate the stiffening means from flexible material such as hook and loop fastening strips so that the stiffening means can also function as a secondary safety securing means.
A further object of the present invention is to provide an improved occlusive cuff having partial fluting to reduce the tendency of the cuff to roll, comprising: an inflatable bladder formed from two sheets of flexible plastic material of substantially the same size and shape and having proximal and distal side edges and two end edges and sealed along the edges to form an inflatable space, and having a length sufficient for the bladder to encircle the limb at a desired location and overlap on itself around the limb; bladder securing means for securing the overlapping bladder around the limb while the bladder is inflated; and partial fluting means comprised of a number of seams which further join together the two sheets of plastic material forming the bladder, and which have preselected locations, distances from the end edges, and lengths from the respective side edges to constrain the shape of the bladder, thereby reducing the tendency of the bladder to roll along the longitudinal axis of the limb when inflated.
The applicant is aware of the following United States patents which are more or less relevant to the subject matter of the applicant's invention.
______________________________________ 5,048,536 9/1991 McEwen 128/748 4,869,265 9/1989 McEwen 128/774 128/327 4,770,175 9/1988 McEwen 128/327 4,605,010 8/1986 McEwen 128/686 4,479,494 10/1984 McEwen 128/327 128/682 4,469,099 9/1984 McEwen 128/327 128/682 ______________________________________
The applicant is also aware of the following published references which are more or less relevant to the subject matter of the applicant's invention.
M. J. Breault, B. Graham, J. A. McEwen and R. W. McGraw, "Internal pressure distribution in limbs encircled by pneumatic surgical tourniquets." Proceedings of the Canadian Medical and Biological Engineering Conference (Toronto, Canada), 1989, pp. 47-49. PA0 J. A. McEwen, M. J. Breault and C. L. Park, "Development and evaluation of calibrated tourniquet cuffs." Proceedings of the Canadian Medical and Biological Engineering Conference (Toronto, Canada), 1989, pp. 107-108. PA0 J. A. McEwen and R. W. McGraw, "An adaptive tourniquet for improved safety in surgery." IEEE Transactions in Biomedical Engineering, Vol.BME-29, February 1982, pp. 122-128. PA0 J. A. McEwen and G. F. Auchinleck, "Advances in surgical tourniquets." J. Assn. Operating Room Nurses, Vol. 36, 1982, pp. 889-896. PA0 J. A. Shaw and D. G. Murray, "The relationship between tourniquet pressure and underlying soft-tissue pressure in the thigh." The Journal of Bone and Joint Surgery, Vol. 64-A, 1982, pp. 1148-1152. PA0 A. C. McLaren and C. H. Rorabeck, "The pressure distribution under tourniquets." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 433-438. PA0 R. J. Newman and A. Muirhead, "A safe and effective low pressure tourniquet." Journal of Bone and Joint Surgery, Vol. 68-B, 1986, pp. 625-628. PA0 J. A. Shaw, W. W. Demuth, and A. W. Gillespy, "Guidelines for the use of digital tourniquets based on physiological pressure measurements." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 1086-1090. PA0 S. E. Grice et al., "Intravenous regional anesthesia: Evaluation and prevention of leakage under the tourniquet." Anesthesiology, Vol. 65, pp. 316-320, 1986.